Manufacture of molybdenum



Patented Nov. 23, 1948 i MANUFACTURE or MoLYBDENUM Charles V. Iredell, Essex Fells, and Robert .1.

Enrico, Union City, N. J., assignors to Westinghouse Electric Corporation, East Pittsburgh, Pa., a corporation. of Pennsylvania Application April 17, 1946, Serial No. 662,698

10 Claims.

(Cl. 'l5-84) This invention relates to manufacture of molybdenum, and more particularly, to such in which the metal produced has improved properties.

The principal object of our inventiom'genera'llyconsidered, `is to produce molybdenum metal which has improved workability whereby it is more universal in its applications than is the metal manufactured under previous processes, the desired result being accomplished by adding a compound of boron to a molybdenum compound such as an intermediate oxide, or oxides, prior to nal reduction.

Another object of our invention is to reduce such material as molybdenum trioxide and ammonium molybdate to molybdenum by first reducing to an intermediate oxide, doping with a, compound of boron, preferably in the form of boric acid.- solution, and then reducing in hydrogen,

whereby improved metalis produced while the boron is removed as `a hydride. l

A further object of-four invention is to produce metallic molybdenum, by reducing an oxide thereof in hydrogen or other reducing atmosphere, by first doping with from .01% to .5% of boric oxide, the subsequent reduction of the doped oxide resulting in the elimination of the excess boron as a hydride.

Other objects and advantages of the invention will become apparent as the description proceeds.

Referring to Vthe drawing:

Fig. 1 is 'an-axial sectional view of a reducing furnace in which the raw product may be initially reduced to a lower oxide.

, Fig. 2 is a vertical sectional View of a sieve in which the partially `reduced molybendum compoundmay behandledf;

Fig. v3 is a, vertical sectional view of a receptacle illustrating the mixing of the partially reduced molybdenum with a boron compound in the form of a solution of borcacid.

Fig. 4 is a vertical sectional view of the apparatus of Fig. 3,` illustrating the subsequent dryingof the/mixture. i

Fig. 5 is a view corresponding to 4, but

showing the subsequent stirring of the dried material, which is again'dried as in Fig. 4.

Fig. l6 is a view `of a sieve, such as shown in Fig.v 2, through which the dried` materialmay .then be passed. y Y

Fig. 'I is an axial sectional view of a, furnace in which the doped and partially reduced material may be further reduced to metal.

The conventional method of reducing molybdenum compounds, such as ammonium lmolybdate and molybdenumtrioxide, for example to the metal molybdenum, is in an atmosphere of hy- `drogen using either continuous or stationary processes. The temperature is raised according to a predetermined schedule to a high point of 1000 C. to 1100 C. in such operation. Existing processes used pure molybdenum salts or oxide as the raw material.

The reduction described may also be carried out in steps, that is, there may be a rst reduction whereby one of the intermediate oxides of molybdenum, such as molybdenum dioxide, is produced, followed by a second reduction wherein the intermediate oxide is reduced to molybdenum metal. Reference is made to the Rennie Patent No. 2,385,843, dated October 2, 1945, the Rennie Patent No. 2,398,114, dated April 9, 1946, and the Rennie Patent No. 2,402,084, dated June 11, 1946, as illustrating how molybendum has been previously produced from compounds thereof.

The resulting molybdenum powder is pressed in molds and then treated at temperatures slightly below the fusion point, as by passing a heavy electric current through the ingot. The resulting sintered ingot is then worked into a rod by Ii. swaging, and `then into wire by drawing operae tions, or else passed directly through rolling mills to reduce its thickness to the desired extent.

In the above described process, at any .point after the metal has recrystallized, the grains are polygonal and equiaxed, with flat surfaces' along thegrain boundaries. The workability of such molybdenum is definitely limited.

Our proposed method is for the purpose of permitting more drastic working of the resulting metal. In brief, our method consists in doping a compound thereof, preferably the intermediate or purplish-brown oxide or dioxide, obtained after the rst reduction of ammonium molybdate or molybdenum trioxide, with a compound of boron, preferably the oxide, conveniently in the form of boric acid solution. The doping is carried out by intimately mixing the intermediate oxide, or oxides, with the proper amount of boric acid solution. Desirable results were obtained with approximately .5% -boric oxide in molybdenum dioxide. A preferred range is between .01% and .5%, the most desirable part of said range being between .25% 'and .5%.` The resulting doped material is then'reduced to metal, pressed, sintered, and worked to the desired form.

Now referring to the drawing in detail, like parts being designated by like reference characters, it will be understood that While there is shown in Fig. 1 a furnace 2l (and in Fig. 7 a `furnace 35) `which may be in the form ofan alundum or other refractory tube 22 surrounded by a heating coil 23 of molybdenum, tungsten, or other refractory material enclosed in insulating material 24, we may instead satisfactorily use a -gas-'lred furnace in either or both instances,

consisting of a nichrome, duralloy or otherv similar refractory metal tube, heated by gas res. The compound to be reduced, such as ammonium molybdate or molybdenum trioxide, is held in a boat, or boats, 25, preferably of refractory metal and supported either on the tube 22 or on a refractory metal flooring or strip 26 on which it may be moved through the furnace. The treatment of said material in the furnace 22 may be similar to that in accordance with one of the Rennie cases, previously referred to, except that the treatment is not carried to the point where free metal is produced, but merely a lower oxide, or oxides.

The partially reduced material 21 from the boat 25` may then be passed through a preferably twenty mesh sieve 28 to remove lumps, the sifted material received in a receptacle 29, being then placed in a mixing container 3i where it is doped with a compound of boron, preferably as a solution 32 of boric acid. As an example, three kilograms of molybdenum dioxide may be doped with a convenient volume of boric acid. solution containing 26.73 grams of boric acid, which is equivalent to .5% boric oxide. The boric acid may be dissolved in approximately 1/2 liter of distilled water and the resulting solution mixed with the molybdenum oxide, as by a stirrer 33 illustrated in Fig. 3, in order to impregnate each particle. of the lower. oxide with the solution. The resulting paste may then be dried for approximately five hours, as represented in Fig. 4. Then the cake is stirred and broken up, as. illustrated in Fig. and again dried overnight. The oxide is then desirably passed through a twenty mesh sieve 34, as represented in Fig. 6.

The iinal reduction of the doped oxide is desirably carried out in a furnace 35, which may correspond to the furnace 2| said doped material being as in Fig. 1 carried in a container 25a, the difference. being that the temperature is raised sufficiently, as to 1100 C., and maintained there for about ve hours so that not only complete reduction to t-he metal is effected, but the excess boron is removed as a hydride. flow during this treatment is desirably at the rate of about 90 cu. ft. per hour. Judging from the color of the flame of the waste hydrogen which is burned, it takes approximately 1/2 Ihour for the boron. to be removed during this reduction. Any traces of boronremaining after the reducing operation, are eliminated during the treating operation.

Theprocedure followed, after reduction may be the same vas that used with regular material except that working is facilitated.

YOur lexperience with the metal produced in accordance with our invention is thatit will withstand much more drastic working than molybdenum produced in. accordance with conventional methods. For example, a strip of hot rolled molybdenum .030" thick made by ourpresent method will withstandv excessive bending and deforming, whereas the regular molybdenum will not stand such treatment. The theory behind this improved result is that the presence of boron during the active reduction of molybdenum dioxide, or other lower oxide, results in a change in the surface of the individual molybdenum grains which has a desirable eifect on the properties The hydrogen r of the molybdenum metal, insofar as working is concerned. Our theory is that instead of resulting in flat-sided polygonic crystals, after recrystallization .the edges of the grains are slightly curved and there is lsome interlocking therebetween, With the result that recrystallized metal hasgreater strength than when processed in the usual manner. Metal prepared by this method is particularly applicable to the uses wherein molybdenum sheet is bent many times in different directions, while at the same time subject to considerable deep drawing. There are many applications in the electronic industry, where special shapes which necessitate such drastic cold working are required.

In a test, a special ring for an electronic tube was produced. 'Ilhis particular part was made from .02. molybdenum sheet. It was desired to stamp the part, using acomplicated die arrangement which involves very drastic working of the metal, instead of using -spun molybdenum as previously. With metal produced in accordance with thel previous method, it was foundv impossible to get aY single ring formed in the stamping dies. However, with metal produced in accordance with the improved process, good rings were obtained. 4 v

Although we have' described our method involving doping of the intermediate or lower oxide, it will be understoodthat doping of' the trioxide or ammonium molybdate may also be employed and the reduction carried out in one step, although the aforo-described process is the one at present preferred. v

Although preferred embodiments of our inventiton have been disclosed, it rwill be understood that modiiications may bemade within th'e spirit and scope of the appended claims. It will also be understood that we have invented anew product as an improved form of molybdenum in which thejmetal has beenv so treated with a compound of boron that a better bond is provided between the crystals giving increased ductility.

We claim:

1. Th'e method of manufacturing molybdenum, comprising reducing a compound selected from the group consisting of molybdenum trioxide and ammonium molybdate to an oxide lower than said trioxide, doping with av small vpercentage of boric oxide, and reducing in hydrogen, whereby substantially all of the boron is removed as a hydride and the'resulting metal has improved qualities.

2L' The method of manufacturing molybdenum comprising reducing a compound selected from the group consisting of molybdenum trioxide and ammonium molybdate to an oxide lower than said trioxide, doping with ar solution of a small percentag'e of boric acid, and finally reducing in hydrogen, substantially all vof the boron being removed as a hydride.

3. The method of manufacturing molybdenum comprising reducing a compound'selected'from the group consisting of molybdenum trioxide and ammonium molybdateto an oxide lowerv than molybdenum trioxide, doping with a small percentage ofa compound of boron, and finally reducing in hydrogen at a temperature of about 1100 C., whereby substantially al1 of the boron is removed as a h'ydride.

4. The method of manuiacturingmolybdenum comprising reducing a compound selected from the group consisting of molybdenum trioxide and ammonium molybdate to an oxide, lower than molybdenum trioxide, doping with between .01%

moved as a hydride.

6. The method of manufacturing molybdenum comprising reducing a compound selected vfrom the group consisting of molybdenum trioxide and ammonium molybdate to an oxide lower than molybdenum trioxide, doping with about .5% boric oxide, and nally reducing in hydrogen, substantially all of the boron being removed as a hydride.

7. The method of manufacturing molybdenum comprising reducing molybdenum trioxide to a lower oxide, doping said lower oxide with about .5% boric oxide, and finally reducing said doped oxide in hydrogen, whereby substantially all of the boron is removed as a hydride, and metal with improved qualities results.

8. The method of manufacturing molybdenum comprising reducing ammonium molybdate to an oxide lower than molybdenum trioxide, doping said lower oxide with about .5% boric oxide, and nally reducing said doped oxide in hydrogen, whereby substantially all of the boron is removed 6 as a hydride, and metal with improved qualities results.

9. The method of manufacturing molybdenum comprising doping an oxide lower than molybdenum trioxide with a small percentage of a compound of boron, and reducing said doped oxide in hydrogen, whereby substantially all of the boron is removed as a hydride, and metal with improved qualities results.

10. The method of manufacturing molybdenum comprising doping a compound selected from the group consisting of molybdenum trioxide and ammonium molybdate 4with a small percentage of a compound of boron, and reducing said doped compound in hydrogen, whereby substantially all the boron is removed as a hydride, and metal with improved qualities results.

CHARLES V. IREDELL. ROBERT J. ENRICO.

REFERENCES CITED The following references are of `record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,602,527 Gero Oct. 12, 1926 2,221,624 Anderson Nov. 12, 1940 2,253,533 Ruben Aug. 26, 1941 2,385,843 Rennie Oct. 2, 1945 2,398,114 Rennie Apr. 9, 1946 2,402,084 Rennie June 11, 1946 

